That's just some people. I don't know anyone (personally) who does this though. Everyone I know takes the time to sort the problem out.
I am fortunate enough to have a seperate bow for 3D and hunting so I tune my hunting bow exclusively for broadhead flight. My broadhead will not hit with my feild points but the bow is tuned for the tightest groups with the broadheads I shoot. I think the biggest reason people tune the broadheads to the same POI as the feild points is that they only have one bow and want to be able to practice and go to 3D's etc and know that they are hitting where they want to without changing the sight box all the time. That is not to say that I don't think you can't get great flight out of your BHeads by tuning them to your feild points....I just think its a little better to tune the bow for B-heads specifically if you have the luxury of more than one bow.

Chris